The present invention relates generally to computer based apparatus and corresponding computer implemented methods for measurement, calibration, and correction of the performance of systems and their components, and more particularly to quality improvement and process optimization tools for analyzing the performance of systems.
An important aspect of the development process in developing systems for use in various industrial fields is establishing tolerance limits for system components. Tolerance limits, sometimes referred to as upper (USL) and lower (LSL) specification limits, define the allowable deviation of a component from a nominal value. A nominal value is a design, or theoretical value. Much research has focused on designing system components to maintain system performance within specified limits even as performance of system components ranges between upper and lower specification limits. According to traditional arithmetic tolerancing, all the tolerances of system components are arithmetically added together, i.e., stacked up, at the extremes of the component design tolerances to predict a worst case system variation. Another tolerancing technique, statistical tolerancing, attempts to predict probabilities of system performance falling outside specified limits in relation to probabilities of various combinations of out-of-tolerance variations in system components. The aim of these and other tolerancing techniques is to design components such that system performance remains within specified performance limits in spite of variations in component performance.
However, it is not always feasible or economical to design components such that a system performs within its specified limits in the face of worst case system variation, or in spite of predicted out-of-tolerance component performances. For some components, imposing such performance requirements results in the component being prohibitively expensive to manufacture. For other components the desired tolerance is technically or practically impossible to achieve. Furthermore, in some cases the degradation in system performance due to variations in the performance of some components is not significant, while in other cases the effect of component variations on system performance is drastic. Thus, there exist trade-offs to be considered in selecting and tolerancing system components in order to achieve a specified system performance goal. Unfortunately, the various tolerancing techniques available in the prior art fail to provide a disciplined approach for considering system behavior as system performance ranges outside desired performance limits. Without this behavior information, such trade-off decisions are difficult to make and are frequently left to the subjective judgement of the system designer or user.
Therefore, a need exists for apparatus and methods for analyzing the behavior of systems as system performance falls outside specified limits due to variations of components, especially with respect to system xe2x80x9cbrittlenessxe2x80x9d behavior. Brittleness is a system characteristic which describes the extent to which system performance degrades sharply, i.e, xe2x80x9cfracturesxe2x80x9d, as the performance of its components ranges over, and beyond toleranced limits.
The invention provides a computer implemented tool for determining the brittleness of a system with respect to at least one system performance measure. The tool comprises a statistical analyzer configured to receive at least one operating parameter input xe2x80x9coxe2x80x9d, and to provide at least one performance function output, xe2x80x9cfxe2x80x9d. The performance function output f provides an indication of system performance as a function of system operating parameter input o. A brittleness analyzer is coupled to the performance function output and is configured to provide a brittleness output based upon performance function f.